Self-Trapped Excitons or Bi<sup>3+</sup> Ions for Broad Emission in a Lead-Free Double Perovskite? Hearing What Pressure Says.
basic_science · Level V
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- Record sourced from PubMed, PMID 40437766.
- Also identified by DOI 10.1021/acs.nanolett.5c01709.
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Abstract
The broad emission origin of lead-free double perovskites with ns<sup>2</sup>-metal ion doping remains a long-standing controversy. Herein, pressure is introduced as a robust tool to determine the mechanism of broad emission from Cs<sub>2</sub>AgIn<sub>0.9</sub>Bi<sub>0.1</sub>Cl<sub>6</sub> nanocrystals (NCs). The negative correlation between the crystal field strength and broad emission wavelength under compression corroborates that the broad emission is indeed attributed to the radiative recombination of self-trapped excitons, ruling out Bi<sup>3+</sup> emission from <sup>3</sup>P<sub><i>n</i></sub> (<i>n</i> = 0, 1, or 2) to <sup>1</sup>S<sub>0</sub> as an alternative mechanism. The broad emission is composed of two types of self-trapped states due to the different structures of BiCl<sub>6</sub>-AgCl<sub>6</sub> and InCl<sub>6</sub>-AgCl<sub>6</sub>. The abnormal emission enhancement within the range of 5.01-10.01 GPa results from the local distortion of BiCl<sub>6</sub> octahedra that increases the exciton-phonon coupling strength. Our study elucidates the long-term dispute about the origin of broad emission in Cs<sub>2</sub>AgIn<sub>0.9</sub>Bi<sub>0.1</sub>Cl<sub>6</sub> NCs, representing a significant step forward in the precise design and synthesis of targeted lead-free double perovskite materials.